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Spectroscopie de photoionisation d’atomes et molécules en phase gazeuse aux échelles de temps femtoseconde et attoseconde

Dominique Platzer 1 
1 ATTO - Attophysique
IRAMIS - Institut Rayonnement Matière de Saclay, LIDyl - Laboratoire Interactions, Dynamiques et Lasers (ex SPAM)
Abstract : In this work are studied atomic and molecular systems in the gas phase using time-resolved electron pump-probe spectroscopy on the femtosecond (1 fs = 10⁻¹⁵ s) and attosecond (1 as = 10⁻¹⁸ s) timescales on the SE1 beamline of the ATTOLab platform. First, the femtosecond dissociation of methyl iodide following the absorption of one UV photon was investigated by Auger spectroscopy and multiphoton ionization (ATI-IR). In the latter case, a relaxation dynamic with 75 fs caracteristic time was evidenced for the part of the nuclear wavepacket confined to small internuclear distances. Second, the attosecond ionization dynamics of argon were studied over a large spectral range including Cooper minima. This study required: (i) a coherent light source in the extreme ultra-violet (photon energy in the 10-100 eV range) based on high harmonic generation and producing attosecond pulse trains, and (ii) an electron interferometry technique giving access to the spectral phase of the photoemitted wavepackets. The latter are used to extract the attosecond photoemission time delays that can be interpreted as the time necessary for the electron to escape from the atomic potential. Strong variations of the time delays were observed between the 3s and 3p valence shells, revealing important electronic correlation effects, like the presence of shake-up ionization channels. To be able to reconstruct the complete movie of the photoionization process, one needs to add spatial information to the spectral/temporal measurements. Two-photon resonant ionization of helium through the 1s3p state was then studied, using a velocity-map imaging (VMI) spectrometer instead of the angularly-integrating magnetic-bottle electron spectrometer used in the previous studies. An extremely fast spectral phase shift was measured, quite homogeneously up to 45° emission angles, thus giving a more complete view of the process. Finally, a new VMI spectrometer was designed, built and installed on the beamline. Its main specifications (energy range and resolution) were optimized for attosecond spectroscopy, mainly through the development of a new electrostatic lens.
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Submitted on : Friday, January 29, 2021 - 12:10:38 PM
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  • HAL Id : tel-03125285, version 1


Dominique Platzer. Spectroscopie de photoionisation d’atomes et molécules en phase gazeuse aux échelles de temps femtoseconde et attoseconde. Physique Atomique [physics.atom-ph]. Université Paris-Saclay, 2020. Français. ⟨NNT : 2020UPASP088⟩. ⟨tel-03125285⟩



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